Page 116 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

chapter 5

Quadcopter Propulsors

Introduction

As the title indicates, this chapter’s discussion will encompass the three elements that
produce the thrust that propels the quadcopter into the air: the propeller, the motor, and the
electronic speed controller (ESC). Each one depends on the other two; and without each doing
its part, there will be no thrust created, and the quadcopter will remain stationary on the
ground. Each element will be discussed separately; however, I will try to show how they are
each tied to one another and will identify their limitations and the constraints they impose
on each other.
The chapter will also present a demonstration of two programs that will allow you to
further explore your current propellers and motor/ESC combinations, along with possible
future propeller upgrades.
I will begin by discussing the motor, an element critical to quadcopter performance and
one most people are familiar with.

Motors

Direct current (DC) motors are nearly universally used in R/C aircraft, helicopters, and
multirotor craft. The two main DC motor types are brushed (BDC) and brushless (BLDC).
Brushless motors are preferred for use in quadcopters because they do not use carbon
brushes, which makes them much easier to maintain. They also rotate at very high speeds,
as compared to brushed motors, and produce less electrical noise. One of the Elev-8 BLDC
motors, a model A2212/13T 1000KV, is shown in Figure 5.1.
The 1000KV in the model name means that the motor is designed to rotate at 1000 r/min
per volt applied to the motor. Thus, an ESC that is powered by a fully charged three-cell
LiPo battery producing over 12 volts could theoretically rotate the motor at a maximum of
12,000 r/min. In reality, the maximum rotation is about 7000 r/min for the Elev-8, since that
is about as fast as the Slo-Flyer propellers can efficiently rotate. In addition, a motor turning
a propeller load will typically have an approximately 600-r/min-per-volt rating, which
equates nicely with the maximum 7000 r/min at roughly a 12-V supply voltage.
BLDCs used in the Elev-8 are also unique in that the rotors are on the motor exterior,
while the stators are fixed on the inside of the motor. This type of motor is also known as an

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